Species composition of Cyanoprokaryota in the summer phytoplankton of 55 lakes and reservoirs, sampled in Bulgaria in the years 2018, 2019, 2021 and 2023

Abstract

The paper presents detailed results on cyanoprokaryote diversity in the summer phytoplankton of 55 lakes, small and large reservoirs sampled in Bulgaria in the frame of three joined projects related to algal blooms threat to human health and national security. The phytoplankton of twenty from these selected waterbodies was sampled for first time. In total, 185 species and one variety from 55 genera have been identified, 54 of which (29%) were novel for the country. The average contribution of cyanophytes to the phytoplankton per site was 8 species (or 44% of the total biodiversity), reaching in some sites 80%. According to the morphology, the recorded algae were distributed as follows: 83 coccal, 52 non-heterocytous filamentous and 51 heterocytous filamentous cyanoprokaryotes. Their average contribution to the phytoplankton diversity was estimated as 4 coccal, 2 non-heterocytous and 2 heterocytous species per site. Most of the cyanoprokaryote species (94, or 51%) were recorded only once, even in the case of wetlands and sites which have been repeatedly visited during all sampling campaigns. These 96 species embrace 39 coccal, 23 non-heteroctous and 32 heterocytous forms. No species was found in all studied waterbodies. The most widely spread species were Microcystis aeruginosa (19 records), Planktolyngbya limnetica (17 records), Aphanizomenon klebahnii (16 records), Microcystis wesenbergii (16 records), Aphanocapsa delicatissima (13 records), Cuspidothrix issatschenkoi (12 records), Coelomoron pusillum (11 records), Pseudanabaena limnetica (11 records), Anagnostidinema amphibium (10 records), Raphidiopsis raciborskii (10 records), Limnococcus limneticus (10 records), and separate cells of Microcystis as well (15 records). The record of the chytrid parasite Rhizosiphon anabaenae on separate trichomes of Sphaerospermopsis aphanizomenoides is described.